1. Field of the Invention
This invention relates to drill strings. More specifically, the invention relates to apparatus and methods for estimating the dynamic behavior of the drill strings.
2. Description of the Related Art
Various types of drill strings are deployed in a borehole for exploration and production of hydrocarbons. A drill string generally includes drill pipe and a bottom hole assembly. The bottom hole assembly contains drill collars, which may be instrumented, and can be used to obtain measurements-while-drilling or while logging, for example.
While deployed in the borehole, the drill string may be subject to a variety of forces or loads. Because the drill string is in the borehole, the loads are unseen and can affect the dynamic behavior of the drill string. An immediate result of the unseen loads may be unknown. If the loads are detrimental, then continued operation of the drill string might cause damage or unreliable operation.
Testing of the drill string may be performed to simulate the loads affecting the drill string. However, the testing may not be able to simulate the same type of loads experienced in the borehole. Field testing can be conducted to determine the loads, but field testing can be prohibitively expensive or inaccurate.
Therefore, what are needed are techniques for estimating the dynamic behavior of a drill string downhole.